You've finally decided to move all your email online to Google's web-based service, Gmail. Great! But what about messages still going to your old email address(es)? You don't have to notify all your contacts that your email address has changed—again. Gmail is not only an email host, it's an email client, which can fetch mail from any number of external services and consolidate it all right there in your Gmail inbox. Here's how to move your email to Gmail without missing a single message from an existing account.